The main causes for the high mortality and morbidity in type 1 diabetes (T1D) are microvascular and macrovascular complications but their mechanisms remain to be defined. Tight glycemic controls in T1D substantially reduced the burden of chronic microvascular and acute complications, but not macrovascular complications. Since proteins are key functional molecules that are closely regulated by insulin, we will identify the individual proteins in the circulation affected by T1D. Although the overall impact of diabetes on protein metabolism has been reported, information on the individual proteins involved is largely unknown. The identification of these proteins will potentially lead to the discovery of markers and/or risk factors for T1D and its complications. We will identify plasma proteins whose concentrations or synthesis rates are altered during both poor and tight glycemic control in T1 D patients using high resolving power mass spectrometers and in vivo isotope labeling, respectively. Based on the preliminary results, we hypothesize that systemic insulin treatment, while achieving glycemic control, may still result in altered synthesis of many proteins in T1 D patients compared to non-diabetic controls. We emphasize the importance of measuring both abundance and synthetic rates in this project, in order to identify the proteins with no detectable alterations in concentrations, but with apparent changes in synthetic rates between different states. The Phase I (R21) is designed to test the feasibility and to refine the analytical approaches. Studies will be performed in a limited number of subjects (T1D and non-diabetic controls) during controlled, short-term interventions. The Phase II studies (R33) will be conducted in sixty T1 D and 30 controls in the clinical setup, and the analysis will be confined to only the candidate proteins identified in Phase I. The studies will not only identify the proteins which are altered between poor and tight glycemic controlled states, but also the proteins which are different in T1D compared to non-diabetic controls and can not be normalized despite of tight glycemic control. These studies are anticipated to form the basis of more elaborate mechanistic studies in the future and hopefully will lead to alternative therapeutic approaches for T1 D.